The present invention relates to a coating device for a paper or board web, and particularly to a guide for the discharge of coating that overflows from the coating application chamber of the device.
A coating device of the type with which the invention may be used is known from Federal Republic of Germany Utility Model 91 06 311. Coating material is flowed from a source against a web moving past an application chamber that is typically pressurized. That coating device includes a guide member which forms a slot for the passage of discharging coating material. The slot is located at the web of material at the place where the web is being guided past the slot by a backing roll. The slot is of substantially constant width off the web and has a relatively long length in the direction of travel of the web. A coating material exit channel or discharge channel is provided at the web entrance end of this slot, because in this device, the web is moving counter to the discharging coating material flow. A feed channel for the coating is provided on the other end of the slot where the doctor element is located. In the discharge channel, i.e. at the start of the slot, there is a throttle plate which forms a throttle slot for regulating the discharge of excess coating composition on the web of material. Very large excess quantities of coating material are required here, as compared with the weight of coating remaining on the web, in the event that this device is used as a predosing device, due to the relatively large slot.
Ordinary dip rolls are also known for use as predosing devices which apply excessive coating composition in a transfer slot to the web of material at the place where the web is guided by a backing roll. However, relatively large problems may arise with higher web speeds, particularly in or at the transfer slot.